GAS-EXCHANGE, WATER RELATIONS, AND DRY-WEIGHT PARTITIONING DURING ROOT INITIATION AND DEVELOPMENT OF POINSETTIA CUTTINGS

Gas exchange, water relations, and dry; weight partitioning of shoot t ip cuttings of 'Eckespoint Lilo Red' ('Lilo') and 'Gutbier V-10 Amy Re d' ('Amy') poinsettia (Euphorbia pulcherrima Willd. ex Klotzsch) were studied during the initiation and development of adventitious roots, N et photosynthesis (A) and stomatal conductance (g) of cuttings were in itially low and remained low until root primordia formation, Foliar re lative water content (RWC) and osmotic potential (psi(pi)) increased u pon formation of root primordia, Following formation of root primordia (2 days before visible root emergence) and concurrent with increasing RWC and psi(pi), g increased, As roots initially emerged, A and g inc reased rapidly and continued to increase with further root primordia d evelopment and subsequent emergence of adventitious roots, Cutting ste m and leaf dry mass and leaf area increased during the first few; days after sticking cuttings, During primordium development and initial ro ot emergence, the highest percent increase in dry weight was accounted for by basal stem sections, All cuttings of both cultivars rooted and had similar root numbers after 23 days, but 'Lilo' cuttings had, 15% better rooting and 44% more roots than 'Amy' after 15 days, This resea rch supports the hypothesis that formation and elongation of root prim ordia coincides with increased gas exchange in poinsettia cuttings, an d that gas exchange can be used as a nondestructive indicator of adven titious root development.